From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Anholt Subject: Re: [PATCH 3/4] spi: bcm2835aux: set up spi-mode before asserting cs-gpio Date: Wed, 10 Feb 2016 10:59:29 -0800 Message-ID: <878u2s2xym.fsf@eliezer.anholt.net> References: <1455041435-8015-1-git-send-email-stephanolbrich@gmx.de> <1455041435-8015-4-git-send-email-stephanolbrich@gmx.de> <87d1s54f7f.fsf@eliezer.anholt.net> <20160210080149.GQ13270@sirena.org.uk> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha512; protocol="application/pgp-signature" Cc: stephanolbrich-Mmb7MZpHnFY@public.gmane.org, Stephen Warren , Lee Jones , linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-rpi-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org To: Mark Brown Return-path: In-Reply-To: <20160210080149.GQ13270-GFdadSzt00ze9xe1eoZjHA@public.gmane.org> Sender: linux-spi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: --=-=-= Content-Type: text/plain Mark Brown writes: > On Tue, Feb 09, 2016 at 03:49:24PM -0800, Eric Anholt wrote: > >> This patch surprised me. I would have thought that the solution was to >> just write the updated CNTL bits for CPOL and wait a moment whenever it >> changes. The CS only gets asserted later on when we get some data in >> the TX FIFO, so I think you're just reducing the chance of losing the >> race to get our inverted clock noticed by the device before the CS gets >> asserted. > > We support (and generally want to use since hardware chip selects are > often very limited in what they do) chip select on GPIO. Oops, this makes more sense now. Subject even mentioned gpio, and a GPIO CS must be getting set around the transfer_one call. I'll be ready to send an r-b for a v2 with the speed update bug fixed (unless transfer speeds are guaranteed to be constant between a prepare and unprepare). --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBCgAGBQJWu4iRAAoJELXWKTbR/J7oZmQP/33+6e1xh2rNOafO6IThppcE tfUMCXfyilIjFaPovx29rRBgyQOd8xVoa1M5OVKo3zbVD2RqgL6JPN2lJ1f4f7Dd 8vKlWsg9kZCc/RAdZmPAWUswQYP/puALwHe9a69PrJUumN7pb9BHwuvWKyxJ+7vB garLS0OYW7EYX0zjX7vYbKtL3DTbeO/sBoiHgHrZGDq4XoE40fxRkO7uUme5NvhU FpZLWDxbd/lpdAukMfKdHCCrPgAhQNX+Sa6/0dUkM3j3cn1NTHCG7jb8Q8JkI+vU SO12X3tDrzcGMWUM4KJY9P3J0lWWQC6z/px8y4cV4zbvrfVaqPq55uQtBpLfij5z gSZhGMvlGjqltuCOmHFSyuTvjb9UBdYITOx+QrA41zceq8c0/7jyWqWSeJfDu/rg Mm5uzgnGMUKmrEZtC8nqiFW4lOzUfeEwzDpOo/G2aMbuFA8tlfr2+fHtzyZHJ8au vBW79h5iG9hYReUsdb5+yO0jUPx8Okc0o70W6GFeW+4c0XMcqYEKeZPU06JdGoTF U73os+mYeDLoqcWNfD4iAq5POG0+aNZd7AxC/2Jf0p91pYNDDSrV3CuAPQNInUHr mZDItWRKdqfbnS0YJUFnemjGDVHh7URzB6TFUpaGdxnd91OGs0JprmlcHY78K6fF D9t4p+nAJZjHh+nwiw2G =br/N -----END PGP SIGNATURE----- --=-=-=-- -- To unsubscribe from this list: send the line "unsubscribe linux-spi" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html